FIG. 5a and 5b show a conventional radiowave receiving array antenna wherein reference numeral 1 designates a lower grounding conductor, numeral 2 designates a feeder circuit board, numeral 3 designates an upper grounding conductor, numerals 4 designate supporting plates, numerals 5 designate low noise amplifiers, numerals 6 designate power source lines for the low noise amplifiers, numeral 7 designates a number of radiation elements, numeral 8 designates a feeder circuit, numerals 9 designate metal pins and numeral 10 designates a number of radiation windows.
In the operation of the conventional array antenna, radiowaves received by the radiation elements 7 in the feeder circuit board are synthesized by the feeder circuit 2, the synthesized signal is amplified by the low noise amplifiers 5, and then, is supplied to a receiver. In the feeder circuit 2, a loss of electric energy produces noise, whereby the quality of an electric signal is deteriorated. When the level of deterioration exceeds an allowable range, it is necessary to divide the antenna into sub-arrays and to insert the low noise amplifiers 5 in each sub-array. Namely, influence by a loss produced in the feeder circuit from the low noise amplifiers 5 to the output terminals of the antenna can be reduced in inverse proportion to the gain of the low noise amplifiers 5 by inserting a plurality of low noise amplifiers 5 in the feeder circuit 2. In order to insert the low noise amplifiers in the feeder circuit 2, it is necessary to mount the low noise amplifiers 5 on the back surface of the lower grounding conductor 1 and to connect the low noise amplifiers 5 to the feeder circuit 2 by using metal pins 9 or the like.
The conventional radiowave receiving array antenna having the construction described above had disadvantages as follows. The structure for connecting the low noise amplifiers and the feeder circuit is complicated to thereby increases cost. Further, since the low noise amplifiers are mounted on the back surface of the lower grounding conductor, the thickness of the antenna device is increased. When the array antenna is prepared for outdoor use, a cover for protecting the low noise amplifiers is additionally needed, whereby the construction is further complicated and cost is further increased.
Accordingly, it is an object of the present invention to reduce the radiowave receiving array antenna increase with respect to the mounting of the low noise amplifiers.